Patent Number: 6,794,827

Title: Multiple ballasts operable from a single DC bus

Abstract: A plurality of lighting ballasts (12, 14, 16) draw power from a single DC bus signal. A power factor correction circuit (10) rectifies and smoothes AC power to produce the DC bus signal. In order to prevent damage to the ballast (12) when a lamp (18) dies or is removed, the ballast (12) includes an AC switch that senses damaging conditions and responds by changing a resonant frequency of the ballast (12). The AC switch operates in 2-3 second cycles. While it is operative, it shunts current away from inductors (38, 40) of the ballast (12) causing a resonant frequency of the ballast (12) to change. At the end of the cycle, the switch turns off, but if a load fault is still present in the ballast (12) it activates again. Preferably, the AC switch has a response time of approximately 500 .mu.s.

Inventors: Nerone; Louis R. (Brecksville, OH), Oberle; Joseph C. (Chagrin Falls, OH)

Assignee: General Electric Company

International Classification: H02M 1/00 (20060101); H05B 41/28 (20060101); H05B 41/285 (20060101); H05B 037/02 ()

Expiration Date: 09/22016